A dendrochronological assessment of two South African Widdringtonia species

Abstract

In southern Africa long-term regional rainfall data sets are very limited such that the variability of rainfall across the region is poorly understood. With available climate records so limited the development of strong proxy records are vital to develop drought management plans. In our continuing efforts to develop such proxy records we present the results of an investigation into the dendrochronologlcal potential of Widdringtonia nodiflora and Widdringtonia schwarzii. We sampled W. schwarzii, from the area it is endemic to, the Baviaanskloof wilderness area, in the Langkloof region of the Eastern Cape Province. Widdringtonia nodiflora samples were collected from the Grootvadersbosch Nature Reserve near Heidelberg in the Western Cape Province. The results Indicate that inconsistencies in ring width combined with poorly defined ring boundaries and converging rings make cross-dating between different trees from the same locality an impossible task for both species using manageable sample numbers. Without cross-dating, chronology development is an equally impossible task for both W. nodiflora and W. schwarzii. As with W. cedarbergensis, W. schwarzii may avoid drought stress by accessing deep water. This may explain the many false rings and poorly defined ring boundaries apparent in this species. This study concludes the dendrochronological assessment of all of the Widdringtonia species with only two South African conifers not evaluated (Podocarpus henkelii and P. elongatus). Widdringtonia cedarbergensis is the only South African conifer that has been successfully cross-dated, however, there are no significant correlations between ring width indices and climate variables for this species.